There are two services in-game. The server and client (player).
The server communicates with all clients but the client can communicate with only the server. The basic game has only client side, the server was added by the Mod makers.
In the case of the construction traffic lights on the client side (what I personally don't believe), it won't communicate with the server - only you will be able to see (like at the gates near Paris). That means every player will see different.
I think it was maybe only troller or a reckless user who didn't pay enough attention to the traffic lights.
Test this with your friends, if it's only on the client side (as I said in the first part) you should report this bug. :))